Synthesis of [11C-methyl]-(-)-OSU6162, its regional brain distribution and some pharmacological effects of (-)-OSU6162 on the dopaminergic system studied in the rhesus monkey by positron emission tomography

Pharmaco-fMRI in Patients With Traumatic Brain Injury: A Randomized Controlled Trial With the Monoaminergic Stabilizer (-)-OSU6162

OBJECTIVE

To examine the effects of monoaminergic stabilizer (-)-OSU6162 on brain activity, as measured by blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI), in patients in the chronic phase of traumatic brain injury suffering from fatigue.

SETTING

Neurorehabilitation clinic.

PARTICIPANTS

Patients with traumatic brain injury received either placebo (n = 24) or active treatment (n = 28). Healthy controls (n = 27) went through fMRI examination at one point and were used in sensitivity analysis on normalization of BOLD response.

DESIGN

Randomized, double-blinded, placebo-controlled design.

MAIN MEASURES

Effects on BOLD signal changes from before to after treatment during performance of a fatiguing attention task.

RESULTS

The fMRI results revealed treatment effects within the right occipitotemporal cortex and the right orbitofrontal cortex. In these regions, the BOLD response was normalized relative to healthy controls at the postintervention fMRI session. No effects were seen in regions in which we previously observed activity differences between patients and healthy controls while performing this fMRI task, such as the striatum.

CONCLUSION

(-)-OSU6162 treatment had influences on functional brain activity, although the normalized regional BOLD response was observed in regions that were not a priori hypothesized to be sensitive to this particular treatment, and was not accompanied by any effects on in-scanner test performance or on fatigue.

Modeling of PET data in CNS drug discovery and development

Positron emission tomography (PET) is increasingly used in drug discovery and development for evaluation of CNS drug disposition and for studies of disease biomarkers to monitor drug effects on brain pathology. The quantitative analysis of PET data is based on kinetic modeling of radioactivity concentrations in plasma and brain tissue compartments. A number of quantitative methods of analysis have been developed that allow the determination of parameters describing drug pharmacokinetics and interaction with target binding sites in the brain. The optimal method of quantification depends on the properties of the radiolabeled drug or radioligand and the binding site studied. We here review the most frequently used methods for quantification of PET data in relation to CNS drug discovery and development. The utility of PET kinetic modeling in the development of novel CNS drugs is illustrated by examples from studies of the brain kinetic properties of radiolabeled drug molecules.

Stimulating and inhibitory effects of the dopamine "stabilizer" (-)-OSU6162 on dopamine D2 receptor function in vitro

The effect of (-)-OSU6162 on the incorporation of GTPgammaS(35) in the membranes of hD(2l)-transfected CHO cells was investigated. In the absence of dopamine the compound exerted a slight but significant stimulating action, suggesting a weak partial agonism. In the presence of dopamine, low concentrations (10 to 100 nM) enhanced the stimulating action of dopamine. This enhancing effect was reversed by higher concentrations of (-)-OSU6162 in a complex biphasic manner. The dopamine-enhancing action is proposed to be mediated by binding to an allosteric site with high affinity and the inhibitory component by a low-affinity binding to the orthosteric site of the dopamine receptor.

The Dopamine Stabilizers (S)-(-)-(3-Methanesulfonyl-phenyl)-1-propyl-piperidine [(-)-OSU6162] and 4-(3-Methanesulfonylphenyl)-1-propyl-piperidine (ACR16) Show High in Vivo D2Receptor Occupancy, Antipsychotic-Like Efficacy, and Low Potential for Motor Side Effects in the Rat

"Dopamine stabilizers" are a new class of compounds that have the ability to reverse both hypo- as well as hyperdopaminergia in vivo. This class, exemplified by the phenylpiperidines (S)-(-)-3-(3-methanesulfonyl-phenyl)-1-propyl-piperidine [(-)-OSU6162] and 4-(3-methanesulfonyl-phenyl)-1-propyl)-piperidine [ACR16] although lacking high in vitro binding affinity for dopamine D2 receptor [(-)-OSU6162, Ki = 447 nM; ACR16, Ki > 1 microM], shows functional actions, suggestive of their interaction. Hence, we evaluated in vivo D2 occupancy of these agents in rats and correlated it to observed effects in a series of behavioral, neurochemical, and endocrine models relevant to the dopamine system and antipsychotic effect. Both (-)-OSU6162 and ACR16 showed robust dose-dependent striatal D2 occupancy with ED50 values of 5.27 and 18.99 mg/kg s.c., respectively, and functional assays showed no partial agonism. Over an occupancy range of 37 to 87% (3-60 mg/kg) for (-)-OSU6162 and 35 to 74% (10-60 mg/kg) for ACR16, we observed both inhibitory (amphetamine-induced locomotor activity) and stimulatory effects (in habituated rats). Haloperidol, over a similar occupancy range (33-78%), potently inhibited psychostimulant activity and induced catalepsy, but it failed to activate habituated animals. In the conditioned avoidance response assay, ACR16 was clearly more efficacious than (-)-OSU6162. In addition, both these compounds demonstrated significant preferential Fos induction in the nucleus accumbens compared with the dorsolateral striatum, a strong predictor of atypical antipsychotic efficacy. The results suggest that dopamine stabilizers exhibit locomotor stabilizing as well as antipsychotic-like effects, with low motor side effect liability, in a dose range that corresponds to high D2 in vivo occupancy.

Positron emission tomography microdosing: a new concept with application in tracer and early clinical drug development

The realisation that new chemical entities under development as drug candidates fail in three of four cases in clinical trials, together with increased costs and increased demands of reducing preclinical animal experiments, have promoted concepts for improvement of early screening procedures in humans. Positron emission tomography (PET) is a non-invasive imaging technology, which makes it possible to determine drug distribution and concentration in vivo in man with the drug labelled with a positron-emitting radionuclide that does not change the biochemical properties. Recently, developments in the field of rapid synthesis of organic compounds labelled with positron-emitting radionuclides have allowed a substantial number of new drug candidates to be labelled and potentially used as probes in PET studies. Together, these factors led to the logical conclusion that early PET studies, performed with very low drug doses-PET-microdosing-could be included in the drug development process as one means for selection or rejection of compounds based on performance in vivo in man. Another important option of PET, to evaluate drug interaction with a target, utilising a PET tracer specific for this target, necessitates a more rapid development of such PET methodology and validations in humans. Since only very low amounts of drugs are used in PET-microdosing studies, the safety requirements should be reduced relative to the safety requirements needed for therapeutic doses. In the following, a methodological scrutinising of the concept is presented. A complete pre-clinical package including limited toxicity assessment is proposed as a base for the regulatory framework of the PET-microdosing concept.

Motor effects of a dopamine stabilizer (GMC1111) in primate models of Parkinson and hemiparkinsonism

The effects on motor behavior of a new potential dopamine stabilizer: 2-amino-6-(N,N-di-n-propylamino)thiazolo[4,5-f]indan (GMC1111) were investigated in common marmosets with 6-hydroxydopamine lesions within the median forebrain bundle (12 unilateral, 6 bilateral). GMC1111 was administered orally or subcutaneously (s.c.) to unilaterally 6-hydroxydopamine lesioned monkeys, either alone or together with s.c. injections of apomorphine (0.2 mg/kg) and the effect on rotational behavior was examined. GMC1111 (0.03-3.0 mg/kg) alone, orally or s.c., did not induce rotational behavior. When apomorphine and GMC1111 were injected simultaneously, rotations were nearly abolished in three monkeys with a baseline apomorphine-induced rotation rate below 13/min, whereas GMC1111 did not modify the rotations in three high-rotating animals (>17/min). Oral administration of GMC1111 (1.0 and 3.0 mg/kg) abolished the apomorphine-induced rotations in another six unilaterally dopamine-denervated monkeys, indicating a good oral bioavailability. A low dose of GMC1111 (0.3 mg/kg) administered s.c. to marmosets with bilateral nigrostriatal lesions produced a reduction of Parkinson symptoms of approximately the same degree as with levodopa/benserazide (15/3.75 mg/kg), while higher doses of GMC1111 were less effective. When levodopa/benserazide was administered together with various doses of GMC1111 (0.3-3.0 mg/kg), the levodopa-induced peak-dose dyskinesias were reduced with the highest dose of GMC1111 (3 mg/kg). Taken together, GMC1111 modifies dopaminergic activity in a normalizing direction. Parkinson symptoms, as well as levodopa-induced dyskinesias are both reduced. This suggests the arrival of another member of the new dopamine stabilizer family.

Coadministration of (-)-OSU6162 with l-DOPA normalizes preproenkephalin mRNA expression in the sensorimotor striatum of primates with unilateral 6-OHDA lesions

The substituted phenylpiperidine (-)-OSU6162 is a novel modulator of the dopaminergic systems with low affinity for dopamine D(2) receptors and potent normalizing effects on l-DOPA-induced dyskinesias. We studied the effects of coadministration of (-)-OSU6162 with l-DOPA on the regulation of striatal preproenkephalin (PPE) and prodynorphin (PDyn) mRNA expression in the primate brain by in situ hybridization histochemistry. Common marmoset monkeys sustaining unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway received l-DOPA/carbidopa, l-DOPA/carbidopa plus (-)-OSU6162, or vehicle over 14 days. In vehicle-treated animals, PPE mRNA levels were markedly increased in the sensorimotor territory of the lesioned striatum. By contrast, a rather uniform lesion-induced reduction of PDyn mRNA levels was found in the vehicle group. Subchronic l-DOPA treatment induced a further increase in PPE mRNA expression in a number of sensorimotor and associative subregions of the denervated striatum. Coadministration of (-)-OSU6162 with l-DOPA partially reversed the lesion- and l-DOPA-induced elevation of PPE expression and, by affecting PPE mRNA expression differentially on the intact and lesioned striatum, markedly reduced the side-to-side difference in PPE mRNA expression. The effects on PPE mRNA expression were apparent throughout the rostrocaudal extent of the putamen and the dorsal portions of the caudate nucleus. l-DOPA treatment resulted in an enhancement in PDyn mRNA expression in all functional compartments of the striatum. Coadministration of (-)-OSU6162 had no apparent influence on these l-DOPA-induced changes in PDyn mRNA expression. The present results suggest that (-)-OSU6162 acts primarily by modifying striatal output via the indirect pathway.

Effects of acute and repeated treatment with a novel dopamine D2 receptor ligand on L-DOPA-induced dyskinesias in MPTP monkeys

(S)-(-)-3-(3-(methylsulfonyl)phenyl)-1-propylpiperidine ((-)-OSU6162) is a phenylpiperidine derivative which exhibits low affinity to the dopamine D2 receptor in vitro. However, in vivo, positron emission tomography scanning studies show that the compound displaces the selective dopamine D2 receptor antagonist, raclopride. We have evaluated, in this study, the effect of (-)-OSU6162, on L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias in a primate model of Parkinson's disease. Five 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated cynomolgus monkeys with a stable parkinsonian syndrome and reproducible dyskinesias to L-DOPA were used in this study. The monkeys were housed in observation cages equipped with an electronic motility monitoring system. They were injected subcutaneously (s.c.) with L-DOPA methyl ester (125 mg per animal) plus benserazide (50 mg per animal; L-DOPA/benserazide) alone or in combination with (-)-OSU6162 (1.0, 3.0, 6.0 or 10 mg/kg, s.c.). Subcutaneous injection of sterile saline was used as control. L-DOPA/benserazide increased locomotion and improved parkinsonism but also induced dyskinesias. Co-administration of (-)-OSU6162 with L-DOPA/benserazide produced a significant reduction in L-DOPA-induced dyskinesias. This improvement in L-DOPA-induced dyskinesias occurred mainly at the onset of the L-DOPA/benserazide effect as reflected by an increase in the duration of the "ON" state without dyskinesias up to 3.4 fold after (-)-OSU6162 co-administration as compared to L-DOPA/benserazide alone. The anti-dyskinetic effect of (-)-OSU6162 was maintained during 14 days and no tolerance to this effect was observed. Our data suggests that (-)-OSU6162 could be of significant clinical value to reduce L-DOPA-induced dyskinesias in fluctuating advanced Parkinson's disease patients.

Motor effects of (-)-OSU6162 in primates with unilateral 6-hydroxydopamine lesions

The effects of the novel compound, (-)-OSU6162 ((S)-(-)-3-methylsulfonylphenyl-1-propylpiperidine), on rotational behavior induced by dopamine receptor agonists was investigated in common marmosets (Callithrix jacchus) with unilateral 6-hydroxydopamine lesions. (-)-OSU6162 per se displayed no effect on the animals' behavior. On the other hand, pretreatment with (-)-OSU6162 attenuated rotational behavior induced by apomorphine (apomorphini hydrochloridum), L-DOPA (3,4-dihydroxyphenylalanine), and the dopamine D2 receptor agonist, quinpirole (trans-(-)-4aR-4,4a, 5,6,7,8,8a,9-octahydro-5-propyl-1H-pyrazolol[3,4-g]quinoline hydrochloride), without inducing motor impairment such as akinesia or dystonia. In addition, treatment with (-)-OSU6162 for 5 consecutive days almost completely abolished the rotational behavior provoked by apomorphine and produced a transient subsensitization of such apomorphine-induced effects after it was discontinued. Moreover, pretreatment with (-)-OSU6162 in two monkeys augmented the rotational behavior elicited by the dopamine D1 receptor agonists, SKF-81297 (R(+)-6-chloro-7,8,dihydroxy-1-phenyl-2,3,4, 5-tetrahydro-1H-3-benzazepine hydrobromide) and A-77636 ((-)-(1R, 3S)-3-adamantyl-1-(aminomethyl)-3,4-dihydro-5, 6-dihydroxy-1H-2-benzopyran hydrochloride). The findings indicate that (-)-OSU6162 can exert indirect state-dependent effects that differentially affect dopamine D1 and dopamine D2 receptor agonist-induced behavior.

Effects of the substituted (S)-3-phenylpiperidine (-)-OSU6162 on PET measurements of [11C]SCH23390 and [11C]raclopride binding in primate brains

The substituted (S)-3-phenylpiperidine (-)-OSU6162 belongs to a novel class of functional modulators of dopaminergic systems. In vivo, (-)-OSU6162 has a unique stabilising profile on dopaminergic functions. In vitro this compound exhibits low affinity for the dopamine D2 receptor, but due to its similarity to neuroleptics on brain dopaminergic neurochemistry and different postsynaptic effects it has been characterised as a preferential dopamine autoreceptor antagonist. To further clarify the effects of (-)-OSU6162 on the postjunctional nigrostriatal dopaminergic system, dopamine receptor binding was measured in rhesus monkeys (Macaca mulatta) by positron emission tomography (PET) using the D1 and D2 dopamine receptor radioligands [11C]SCH23390 and [11C]raclopride respectively, before and during continuous intravenous infusions of(-)-OSU6162. Additionally, the test-retest variability of sequential [11C]SCH23390 scans was estimated. Following the administration of (-)-OSU6162, [11C]raclopride binding in striatum was dose-dependently decreased with a 76% reduction occurring after 3.0 mg/kg per h continuous infusion. Whereas (-)-OSU6162 in the lower doses had no effect on [11C]SCH23390 binding, the highest dose, 3.0 mg/kg per h, increased [11C]SCH23390 binding, which may indicate a potentiating effect on D1 dopamine receptor mediated functions. Thus, in contrast to the conditions in vitro, (-)-OSU6162 produces a high displacement of raclopride from D2 receptors in vivo.

Effects of the substituted (S)-3-phenylpiperidine (-)-OSU6162 on PET measurements in subhuman primates: evidence for tone-dependent normalization of striatal dopaminergic activity

(-)-OSU6162 is a substituted (S)-3-phenylpiperidine derivative which exhibits some affinity to the dopamine D2 receptor family. In vivo, the compound displays a unique normalizing profile on psychomotor activity by an intriguing mixture of stimulatory and inhibitory properties. In the present investigation, some of the effects of (-)-OSU6162 on central dopaminergic function were studied by positron emission tomography (PET) and L-[11C]DOPA in anaesthetized female rhesus monkeys. (-)-OSU6162 displayed a dopaminergic tone-dependent effect with a reduction in the striatal L-[11C]DOPA influx rate in monkeys with high baseline values and an increased striatal L-[11C]DOPA influx rate in animals with low baseline values. Infusion of (-)-OSU6162 for a whole day resulted in a stable effect with no evidence of tolerance. (-)-OSU6162 also stabilized dopaminergic function by attenuating the upregulation of the striatal L-[11C]DOPA influx rate which has previously been shown to occur following 6R-BH4 or 6R-BH4 + L-tyrosine infusions. This "Protean" effect of (-)-OSU6162 on the striatal dopaminergic function corresponds to previous behavioral observations in intact animals and demonstrates a true functional correlation to the measures obtained with L-[11C]DOPA and PET. The normalizing and stabilizing profile of (-)-OSU6162 should be of value in treating a variety of disorders where an underlying dysregulation or disruption of dopaminergic function can be assumed.